Abstract: A dextranase producing strain Altermonas espejiana YSN412 was isolated from a beach mud sample of Lianyungang port. The enzymatic properties of the dextranase AesDEX were analyzed. The culture condition for production of enzyme from the strain was investigated. The optimum temperature and pH value of the enzyme were 30℃ and 8 respectively. After incubation at 30℃ and 50℃ for 2.5h, the remnant relative enzymatic activities were 95% and 14% respectively. The optimum carbon and nitrogen sources were cellobiose and yeast powder respectively. When the concentration of NaCl was 2% (w/w) and the initial pH value was 8, the enzymatic activity of the liquid culture reached its maximum 9U/mL after culturing the strain for 12h. The A. espejiana YSN412 strain isolated and identified in this study produced dextranase quickly and the dextranase AesDEX had a low optimum temperature for enzymatic activity. The enzyme showed the potential to lower the cost and increase the efficiency in industry.